A hyperspectral imager is a known device that is commonly used to examine the spectral, or wavelength dependent, content of an object or scene. (Hyperspectral imagers are also referred to as imaging spectrometers.) In a hyperspectral imager, light emitted or reflected by a given object or scene is imaged onto the entrance of a spectrometer, usually a slit element that transmits a single line image of the object or scene. The spectrometer in turn re-images this light to another location while dispersing this light according to its wavelength in a direction orthogonal to the orientation of the slit element, where it can readily be observed or recorded. In this manner, each line image of the object or scene is decomposed into a two-dimensional data array, and by scanning the object or scene in line-by-line increments, a three-dimensional datacube is formed.
Fluorescence microscopy is used extensively to gain a deeper understanding of varying cellular dynamics. A major impetus towards the widespread application of this analytical tool is the ongoing development of fluorescent proteins, nanocrystals, and organic fluorophores with a range of sensitivities for physiological analytes. Development and application of fluorescent probes has revolutionized studies of cell and tissue physiology. However, to fully utilize the potential information yielded by these probes, detection systems must simultaneously monitor the spectroscopic variations of a combination of fluorophores. This requirement comes from the fact that most cellular responses do not occur in isolation, rather there is a complex sequence of events that occurs in response to cellular effectors. Furthermore, samples of physiological interest often consist of a heterogeneous population of cells, each potentially coupled to other cells and responding to a perturbation with a unique pattern. In order to determine the time sequence of such events with fluorescence techniques, a spectral imaging system must exhibit an appropriate combination of high spatial, spectral, and temporal resolution. Due to the scanning requirements of currently available systems, one or more of these parameters is often sacrificed for the improvement of another. This leads to spatial or temporal ambiguities in the time course of biological processes. These same limitations are also present for endogenous fluorescence signals where there are often unique combinations of different molecules in the sample with unique temporal interactions that are difficult to detect with scanning techniques. In addition, many endogenous and exogenous fluorescence contrast agents photobleach over time and would benefit from non-scanning approaches that can collect the signal over the full integration period. Reflectance and absorption based signals also experience similar detection tradeoffs with scanning based imaging spectrometers.
A growing trend in endoscopic imaging techniques for early and pre-cancer detection has been to enhance their diagnostic capabilities by improving the spectral content of their images. Spectroscopy techniques have demonstrated that endogenous cancer bio-markers such as nicotinamide adenine dinucleotide (“NADH”), flavin adenine dinucleotide (“FAD”), collagen, and oxy- and deoxy-hemoglobin have distinct fluorescence and reflectance based spectral signatures. These molecular bio-markers may serve as important indicators in identifying pre- and early cancerous regions to more traditional morphologic and architectural features. Imaging spectrometers have been proposed but drawbacks have limited their use as affordable, real-time screening tools. The main limitation of these approaches has been their reliance on expensive tunable filters, such as liquid crystal or acousto-optic, for acquiring the increased spectral bandwidth. Not only are these filters prohibitively expensive, but they also delay imaging acquisition times (>about 23 seconds) due to the serial fashion in which the spectral data is collected. Snapshot techniques such as the Computed Tomography Imaging Spectrometer (“CTIS”) avoid this limitation, however these have long post-acquisition processing (about 30 to 60 min) which is also ill-suited for in vivo imaging.
Remote sensing is a valuable tool for acquiring information from dangerous or inaccessible areas such as war zones, glaciers, ocean depths, hurricanes, gas plumes, biological weapons, etc. Imaging spectrometers enhance remote sensing techniques providing critical information based on subtle spectral features from a sample. These devices are often used on vehicles that travel at high speeds, such as satellites and planes, consequently requiring fast data collection. Scanning-based approaches often compromise on image size, contrast, and/or spectral resolution to meet these fast temporal acquisition requirements. In some cases, the event in question, such as verification that a missile has hit its target, transpires so fast that it is virtually impossible for scanning approaches to be used, such as verification that a missile has hit its target. Therefore, non-scanning, snapshot spectral imaging techniques would be desirable.
Food inspection plays an important role in assuring the quality of the food that is consumed within our country. However, this process is typically a human-based manual observation of the food for visually-apparent detects. This approach has several limitations, including the fact that many defects are not observable with the human eye. It can also be a slow process, prone to human errors and sampling inaccuracies. Spectral imaging techniques can play a significant role in this area by being able to evaluate food for multiple defects in a quick and quantitative manner based on unique spectral signatures. To have minimal impact on the time to market, these inspection stations must acquire and analysis information very fast, limiting the usefulness of scanning based approaches.